Computer Numerically Controlled (CNC) machines are well know. Such CNC machines typically control a material remover and include milling machines having various numbers of axes about which the material remover can be moved. In such milling machines, the material remover is a rotating element that is moved across the block of material from which a part is being manufactured.
As such, the CNC machine has, what may be referred to as, a cutting path programmed into it along which the material remover is moved. It will be appreciated that the length of time that it takes to make a part from the block of material is governed by the length of the path and the speed at which the material remover is moved along that path. Thus, the more efficiently the path can be planned then the quicker the part can be manufactured.
It will also be appreciated that the machine controlling the material remover will have physical constraints upon its movement. For example, the motors controlling motion of the material remover will only be able to apply a finite amount of force and torque; the material remover will be able to remove a maximum amount of material in a pass, etc. Processing circuitry of the machine tool that processes the cutting paths and/or controls motion of the material remover will also have a maximum rate at which it can process instructions and this maximum rate, as with the physical constraints, will vary between machine tools.
Therefore, it is possible for a desired cutting path (ie one that a program wishes the material remover to follow) to request that the material remover exceed either or both of the physical constraints or the processing constraints which will typically lead to the cutting not being performed as desired. If the constraints are exceeded the machine will typically execute a compromise which may be due to physical limitation (for example the acceleration of the material remover will simply be limited to what is possible to achieve) or software causing the material remover to move may adapt the cutting path to something that is achievable.
As such, providing a cutting path that the material remover cannot execute as intended can affect the speed at which the part can be made but it can also affect the quality of the finished part since the compromises that are employed can lead to unexpected results.
FIGS. 1a and 1b show details of a material remover 204 with various parameters marked thereon which are useful in explaining the process of linear milling as would be performed by a machine tool such as a CNC milling machine as shown in FIG. 2.
The cutting conditions of the material remover 204 are mostly affected by the spindle speed N, the feedrate F and the amount of material the tool is removing which is defined by the depth of cut d and the stepover s. It will be seen that stepover s is measured in a radial direction of the cutting tool whereas the depth of cut is measured in an axial direction of the cutting tool.
It is common practice to adapt these values depending on the properties of a block of material 202 being machined (nature of the material, its hardness, etc.) but also depending on the properties of the material remover 204 (tool size and shape, material it is made of, number of teeth, etc.). Tool manufacturers (ie manufacturers of the material remover 204) typically provide charts detailing the maximum safe parameter values that can be used for a specific material remover 204 when cutting a block of material 202 of a given type.
Embodiments can achieve efficient machining of a particular part by setting these values so as to remove as much material as possible in the least possible amount of time. Common sense dictates that this equates to finding a combination of the parameters outlined in relation to FIG. 1a (F, N, s and d) such that the material remover 204 is cutting as close as possible to its capabilities.